From German Examined, Published Patent Application DE-AS 1 027 959 of Witzig et al, a turret-type machine tool with a workpiece support in the form of a circular switching table for a plurality of machining stations is known. The workpiece holders located on the circular switching table can be rotated automatically about their own axis during the onward indexing of the table in such a way that the workpieces are aligned parallel to one another in the various machining stations. Besides the circular switching table, machining units assigned to the various machining stations are provided, formed as multiple-spindle heads; their machining spindles, carrying various workpieces, can be positioned with respect to the workpiece support. The arrangement is such that in each machining station, with the tools inserted into the machining spindles of the multispindle head, various operations can be performed simultaneously for a number of identical workpieces corresponding to the number of machining spindles; these workpieces are clamped to workpiece holders that succeed one another over the circumference of the circular switching table. However, a machine of this kind can be used only to machine special workpieces, such as fittings, in which relatively simple machining operations are to be performed and that have the characteristic that they can be take care of in groups by the machining spindles of a multispindle head.
Another turret-type machine tool, known from U.S. Pat. No. 4,473,930, Bezner et al, assigned to the assignee of this application, to which German Patent 2 755 755 corresponds, is substantially more universally usable; in it, an incrementally indexable workpiece support, rotatably supported about a vertical axis, is suspended from the top wall part of a rigid and inherently stable and distortion-resistant closed cage, whose bottom wall part is formed like a tub and has a central chip removal opening. The workpiece holders are located on the circumference of the disklike workpiece support. Machining the workpieces clamped thereon is done by machining units that are located in the various machining stations and operate from the side, from above and from below. The workpiece holders are aligned with their axes precisely radially with respect to the workpiece support; that is, the axis intersect the vertical switching axis of the workpiece support. Without additional equipment, the machining spindles inserted into the side walls of the cage can machine the workpieces essentially only from the face end. Machining over the circumference is done by the machining units that work from above and below. In principle, however, the machining spindles of a machining station can machine only the workpiece located in that machining station; they cannot be simultaneously used to machine workpieces in adjacent machining stations as well. Aside from this fact, this turret-type machine tool can in principle, with a view to the housing size, be used only to machine workpieces whose dimensions do not exceed certain values.